A variety of methods are known for dissipating heat in semiconductor devices. An existing method of heat dissipation employs a beryllium oxide (BeO) substrate which has a very high thermal conductivity. In addition, electrical currents may also be conducted by a refractory metallization and solder on the BeO substrate. Disadvantages of such systems include relatively high cost of manufacture, the toxic nature of BeO and relatively high electrical resistance of the refractory metallization. In fact, the use of BeO may not be practical in near future due to anticipated environmental regulation.
Many thermal management methods for semiconductor applications are designed to dissipate heat primarily in the vertical or z-direction underneath the heat generating device. For example, alumina substrates are often placed underneath the heat generating semiconductor chips. The alumina substrates dissipate heat in the vertical or z-direction away from the heat generating chip. Such designs are limited in their ability to dissipate heat laterally, i.e., in the x and y directions. This is because the thermal conductivity of an alumina substrate is low compared to metallic materials and the cross-sectional area of the substrate (thickness) available for conduction in the lateral direction is smaller than the area under the chip for thermal conduction in the z-direction. Systems capable of dissipating heat also in the lateral direction, i.e., x and y directions, have an advantage over systems capable of dissipating heat only in the vertical or z-direction. Dissipation of heat in the x and y directions is an advantage because it provides low thermal resistance paths in addition to the path directly under the heat dissipating device which results in an overall reduction of the device's thermal resistance.
Many semiconductor heat dissipating systems primarily use a large substrate or metal core for dissipating heat. The use of thick films for dissipating heat has not heretofore been seriously considered. Conventional thick films have a thickness in the range of about 0.5 mil to 1.0 mil. It is conventional wisdom to optimize the thickness of such films in the 0.5 mil to 1.0 mil for the intended application. Thicker films are considered to be disadvantageous especially in the cases of nitrogen-fireable copper conductor films where the excessive thickness can lead to improper binder burn-out and can have detrimental effects on solderability and/or adhesion strength. However, it would be desirable to develop a heat dissipating and current conduction system utilizing thick films which is capable of spreading heat in the lateral direction (i.e., in the x and y directions).